I was driving on my scooter behind a car, it was traffic, I used bike lane to pass it, but one of the passenger opened her door, I hit it, little damage for her door, I have no insurance and we didn't make police report, now her insurance agent calls me and ask for money

Bike lanes are for bicycles not scooters and motorcycles... additionally you are technically not allowed to pass on the right in most states of the country. And even when on a bicycle are obligated to follow all the rules and laws of the road. The vehicle in front of you has the right of way... and its your responsibility to look for opening doors.

If its not a lot of money... pay the insurance company but get it all in writing. They can and might take you to court for it.

Unfortunately, you are at fault. You hit her, passing on the right, in a bike lane. Pay the damages and be glad that you didn't have a $300 fine too.

Actually, If this was a marked bike lane, then there is shared fault here and maybe even more on the passenger. By opening a door into a marked bike lane the passenger was blocking the bicyclist right of way. Of course the fact that this was a motor scooter instead of a bicycle may have a bearing. You should have called the police if there was damage.

At this point tell them to sue you if you can't pay.Or at least offer to split the cost since it may have been partially the passenger's fault.